The invention relates to a sealing configuration for sealing off a first region from a second region through which a fluid can flow and which can be kept at different pressures. A differential pressure can be produced between the two regions by the different pressures. The invention relates in particular to a sealing configuration that can be used for sealing in rotary machines, such as electrical rotary machines and thermal fluid-flow machines.
A device for non-contact sealing between spaces of different pressure, in particular for a fluid-flow machine in which shaft leadthroughs between spaces of different pressure have to be provided with suitable seals, is described in European Patent Application No. 0 611 905 A1. The specified device is formed of a labyrinth seal in which step-shaped labyrinth gaps are formed between a rotating part and a stationary part. Sealing tips are disposed in the labyrinth gaps on each of the rotating part and the stationary part, as a result of which a high degree of swirling of a medium flowing through is said to be achieved. The sealing tips between the stationary part and the rotating part are disposed as close to one another as possible, so that there is only a slight radial gap. The sealing tips extend radially in such a way that sealing tips of two adjacent steps overlap. A group of sealing tips can be caulked in place in a corresponding groove through the use of a caulking wire.
Various seals for a turbine stage of a steam turbine are specified in an article entitled xe2x80x9cMaBnahmen zur Modernisierung und Lebensdauerverlxc3xa4ngerung an Dampfturbinenkomponentenxe2x80x9d [Measures for Modernizing and Prolonging the Life of Steam Turbine Components] by D. Bergmann, M. Jansen and H. Oeynhausen, in VGB Kraftwerkstechnik 71, 1991, No. 2, pages 116 to 112. FIG. 13 of the article shows relative leakage-steam flows between a guide blade and a turbine rotor. In that case, recesses are made in the guide blade in some embodiments. The lowest relative leakage-steam flow rates are achieved for labyrinth seals in which sealing tips are disposed on the turbine rotor and on the guide blades in an alternate manner in the axial direction. Efficiency losses of a steam turbine plant can be reduced by an improvement in gap sealing between the turbine rotor and the guide blade.
Austrian Patent No. 362 639 shows a non-contact seal between a part rotating in a space to be sealed off and a stationary part. A ring-shaped sealing body surrounds a shaft leading out of a casing. A pressure medium is stored under a pressure T1 in the casing. The sealing body is pressed by the pressure of the pressure medium in the direction of a sealing surface of the shaft. A gap remains between the sealing surface and the sealing body due to pressure chambers. The height of the gap is firmly preset by choke points which reduce the pressure Tl to a lower pressure in the pressure chambers. An end-wall section of the sealing body, which is opposite the sealing surface, is positioned in such a way that possible tilting of the sealing body is automatically compensated for by a tilt-point displacement.
German Published, Non-Prosecuted Patent Application DE 35 33 829 A1 shows a sealing device with a gas-lubricated mechanical surface seal. Two sealing rings lying opposite one another form a sealing gap through which a gaseous medium flows. A gas lubricating film is obtained at a very specific pressure, and that gas lubricating film keeps the two sealing rings at a distance apart at a defined gap width. During a pressure reduction, one of the sealing rings is pushed back into an open position by a spring force.
It is accordingly an object of the invention to provide a sealing configuration, in particular for a rotary machine, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and which is used for sealing off two regions through which a fluid can flow that are at different pressure levels in order to reduce a leakage flow from one region into the other region, as may be necessary, for example, in thermal fluid-flow machines or electrical rotary machines.
With the foregoing and other objects in view there is provided, in accordance with the invention, a sealing configuration, comprising first and second regions for conducting a fluid flow and/or being filled with a fluid. The regions are to be sealed-off relative to one another and kept at different pressures forming a differential pressure. An opposing surface and a deformation region are provided. A sealing surface is connected to the deformation region and spaced apart from the opposing surface by a sealing gap. The sealing gap has a height to be set by a deformation of the deformation region as a result of a force exerted by the differential pressure.
The invention is based on the concept that, in pressure-carrying machines, such as fluid-flow machines, in particular steam turbines, different pressure levels of the working medium, for example steam or gas, are to be sealed off from one another, or the working medium is to be sealed off from the ambient medium. In the case of known seals between stationary and rotating parts, non-contact seals are mainly used, in particular in steam turbines, due to the high circumferential velocities and the nature of the sealing task. If there are pressure differences, the non-contact seals have an unavoidable leakage mass flow, which leads to losses in output or efficiency of the pressure-carrying machine. The leakage mass flow is substantially determined by the clearances in the seal, e.g. tip-to-tip seals or a labyrinth seal, and by gap widths in seals without tips. In known seals, those clearances are to be constructed in such a way that the loading cases occurring in the machine can be controlled without damage, i.e. without grazing. For example, that applies during normal operation, cold or hot start, when passing a critical speed, during operation of turning gear, and in the event of plant malfunctions. That is because, in the event of grazing, the clearance would be bridged and the rotating component would touch the stationary component. In order to avoid that in every operating or malfunction situation of the machine, the clearances as a rule are dimensioned too generously for the actual operation, that is when there are stringent tightness requirements. On the contrary, for the dimensioning of the clearance, transient processes and the passing of a critical speed as well as the compensation for any production tolerances in size, form and position are decisive. In addition, a reduction in the clearance in known seals in a steam turbine, at high steam pressures and in the case of slim turbine rotors, could lead to gap excitation, which in turn influences the dynamic behavior and may lead to self-excited vibrations. Furthermore, the leakage mass flows which occur in the current seals through the seals of the blade stages in a steam turbine in cylinder type of construction during the re-entry to the blading space cause disturbances in the inflow to the following blade row, e.g. due to incorrect incident flows.
If the differential pressure changes, the height of the sealing gap is changed by a differential-pressure-controlled sealing configuration so that, in particular when the differential pressure is increasing, the height of the sealing gap, i.e. the clearance, is reduced and a considerable sealing effect is thereby produced. The sealing in that case is effected by an interaction of the sealing surface with the opposing surface, which in particular is axial. A considerable sealing effect is achieved in the process by the functioning mode of the deformation region, which undergoes a deformation, in particular an axial elongation, toward the sealing surface when the differential pressure is applied to the sealing configuration. Furthermore, the change in the spacing between the sealing surface and the opposing surface forms a sealing region through the use of which an improved sealing effect is produced with decreasing height of the sealing gap. In addition, with a decreasing height of the sealing gap, an increasing counterforce, in particular an axial force, against the deformation (elongation) of the deformation region can be produced. As a result, the sealing configuration is not only non-contacting but also self-setting.
In accordance with another feature of the invention, at least one sealing element is provided on the sealing surface and/or on the opposing surface and projects into the sealing gap or the sealing surface and/or the opposing surface. This sealing element is preferably disposed on an outer margin of the sealing surface or the opposing surface toward the first region or toward the second region. The sealing element is preferably disposed on the outer margin toward the region having the lower pressure level. In this case, the sealing element may be constructed, for example, as a gap, a projection or a tip. Appropriate shaping of the sealing surface or of the opposing surface, or a geometrical configuration or a spatially distributed material composition of the sealing surface or of the opposing surface which produces a pressure-controlled elastic deformation and a consequent reduction in the height of the sealing gap, is also regarded as a sealing element. The insertion of a suitable sealing element provides for a self-setting sealing configuration in which an increasing counter force, in particular an axial force, counteracting the deformation of the deformation region arises, with decreasing height of the sealing gap (sealing-gap height). This counterforce, with decreasing height of the sealing gap, increasingly counteracts a further narrowing of the gap. Inter alia, this results from the fact that, at a relatively large height of the sealing gap, the fluid flows between the two regions during a pressure build-up and flows through the gap formed by the sealing surface and the opposing surface. In the process, the flow velocity becomes greater, as the height of the sealing gap and the pressure difference become greater. At a supercritical pressure ratio, the velocity of sound may be reached at the narrowest cross section. Due to physical laws, as specified, for example, in Bernoulli""s equation, a reduced static pressure thereby arises in the gap. As a result, the sealing surface is subjected to an action of force (closing force) in the direction of the sealing gap, a factor which leads at least to partial closing of the gap. As the sealing gap becomes narrower, the flow velocity decreases, and the closing force acting on the sealing surface for closing the gap also decreases as a result.
In accordance with a further feature of the invention, the sealing configuration has two sealing elements which are at a distance from one another in the differential-pressure-induced flow direction (main gap direction). One sealing element is preferably disposed in a marginal region facing the region having a lower pressure, and the other sealing element is preferably disposed in a marginal region at the sealing surface or the opposing surface which faces the region having a higher pressure. The sealing element facing the region having a lower pressure preferably leads to greater narrowing of the sealing gap than the sealing element facing the region having a higher pressure. At a reduced height of the sealing gap, the sealing elements disposed on the sealing surface or opposing surface lead to an increase in the pressure in the region of the sealing gap between the two sealing elements. At the same time this results in a reduction in the flow velocity in the sealing gap overall. If the sealing element facing the region having a lower pressure leads to greater narrowing of the sealing gap, the pressure inside the sealing gap approaches the higher pressure. With decreasing height of the sealing gap, this therefore leads to an increase in the counterforce acting on the sealing surface and at the same time to a reduced leakage mass flow.
The sealing configuration can therefore be constructed in a simple manner with regard to construction and material selection, to provide as great a sealing effect as possible within a predeterminable pressure-difference range. In particular, it is possible, within this predeterminable pressure-difference range, for equilibrium to be achieved between the closing force, acting on the sealing surface due to the pressure difference, and the counterforce counteracting the closing force and caused by the gap narrowing. A favorable gap height is set during this equilibrium. As a result, at a smaller pressure difference than the design pressure difference, a somewhat larger gap will arise as compared with the sealing-gap height set in the equilibrium state between the closing force and the counterforce. If there is no pressure difference, the sealing configuration will not be deformed. As a result, the maximum height of the gap is established, and this maximum height, depending on requirements and construction, may be several millimeters for a corresponding machine, in particular in a steam turbine. The sealing configuration therefore has a very narrow clearance, and thus an especially good sealing effect, only at the design pressure difference, in particular during on-load operation of a steam turbine, when there are increased sealing requirements. During the operations heretofore determining the clearance in steam turbines, the sealing configuration has a large clearance, so that grazing of the sealing surface on the opposing surface and thus damage to the machine are avoided.
The sealing surface may be constructed in such a way that it is rigid or flexible (deformable) relative to the design pressure difference. The sealing surface is preferably connected in a rigid or flexible manner through a connection region to the deformation region, in particular to a profile having a U-shaped cross section. The sealing surface may be connected to the deformation region at the region having a lower pressure or at the region having a higher pressure. In a circular-ring-shaped configuration of the sealing surface, this corresponds to a connection at the inside diameter or the outside diameter of the circular ring.
A sealing element may be constructed as a widened portion, a bead, a deformation of the gap-height reduction of the sealing surface, which deformation occurs as a result of the pressure difference, or a sealing strip and/or a sealing tip. One or more sealing elements may be provided both on the sealing surface and on the opposing surface or on both surfaces, in particular in their marginal regions.
In accordance with an added feature of the invention, there is provided a gap-influencing element in addition to or as an alternative to a sealing element. The gap-influencing element is preferably a swirl breaker or a hydrodynamically effective bearing surface. A gap-influencing element allows the flow to be influenced or allows the force equilibrium between the closing force and the counterforce to be influenced in a specific manner. A swirl breaker can be used in particular when the sealing configuration is used for avoiding or reducing gap excitation effects. A hydrodynamically effective bearing surface, which produces a counterforce due to a narrowing media-filled gap, preferably serves to establish the lower limit of the sealing-gap height.
In accordance with an additional feature of the invention, the deformation region, which in particular is movable in the direction of a machine axis, is constructed like a corrugated spring, a bellows, or a series connection of plates subjected to radial bending stress, in particular for enclosing a machine shaft (circular-ring plates). Through application of pressure to the plates on one side as a result of the pressure difference, a deflection occurs, which is of varying magnitude depending on construction and pressure. In this case, the deformation behavior can be implemented for a design pressure difference through the use of analytical computations or commercially obtainable computer programs. Depending on the construction, the calculations are carried out with the margin of the deformation region mounted or clamped. A plurality of plates which are connected one behind the other and form a deformation bellows may be used, in particular, for compensating for relative deformations, as occur in steam turbines, for example. In this case, the individual plates may be connected to one another in a flexible manner at their outer margins or, in particular at high pressure differences, they may be connected to one another in a flexurally rigid manner. It is likewise possible to connect one plate to an adjacent plate in a flexible manner and to another adjacent plate in a flexurally rigid manner. Furthermore, plates having different thicknesses may be provided, in which case, in particular, alternately thick and thin plates may follow one another. The plates are preferably disposed parallel to one another and in particular perpendicular to a machine axis. It is likewise possible to place adjacent plates at an acute angle relative to one another. Of course, both the diameter of the plates across the deformation region and the division, i.e. the distance between two adjacent plates, may vary. In addition to a multiplicity of plates forming a bellows, an individual plate or a plate-shaped component having a sealing surface connected thereto may also be provided.
In accordance with yet another feature of the invention, in particular for use in a rotary machine having a rotating shaft, the sealing surface and the deformation region are constructed in a ring shape, preferably in a circular-ring shape. The sealing gap preferably extends in a sealing plane which, for sealing a radial gap extending along a machine axis, is inclined relative to the machine axis by 70xc2x0 to 110xc2x0. In this case, the sealing gap is preferably perpendicular to the machine axis or to the actual radial gap to be sealed. When the sealing configuration is used, a rotary machine may also be constructed in such a way that a radial gap is dispensed with. This radial gap to be sealed is formed, for example, between a stationary machine component and a rotatable machine component. In this case, the sealing surface is connected either to the stationary machine component or to the rotatable machine component and accordingly the opposing surface is connected to the other respectively machine component.
In accordance with yet a further feature of the invention, the sealing configuration is disposed in a rotary machine, in particular a pump, a turbine, such. as a steam turbine or gas turbine, a compressor of a gas turbine, or in a generator. In this case, the sealing configuration may be connected in series with seals that are already present or may partly or completely replace the latter. When the sealing demands made on conventional seals adjacent the sealing configuration are slight, those conventional seals, in particular for increasing operational reliability, may then be provided with a greater clearance. In this case, the sealing configuration may be used on the side having the higher pressure at a gap to be sealed, so that the pressure inside the gap to be sealed drops, which leads to a reduction in any gap excitation. Deformations caused by existing temperature differences or by transient heat-transfer processes can largely be avoided due to the compact type of construction of the sealing configuration with low mass and the thin-walled construction of the deformation region and the sealing surface. At most slight temperature differences occur over the sealing surface and the deformation region due to the small wall thickness. In addition, in a steam turbine, the steam flowing through the sealing configuration is subjected to choking with only a slight drop in temperature, so that approximately the same temperature is present in front of and behind the sealing configuration. The seal can rapidly follow transient temperature changes due to its comparatively small masses. In addition, even slight radial displacements of the rotating component and the stationary component, which displacements limit the gap to be sealed, do not influence the sealing effect of the sealing configuration.
A ring-shaped deformation region and the sealing surface may be produced by material removal, in particular by machining, by creating or primary forming, by a forming process or by a joining process, as well as by a combination of these methods. The deformation region may be firmly clamped in the stationary machine component or rotating machine component. It is preferably made of a high-temperature-resistant material, in particular a steel, a nickel-base alloy or a cobalt-base alloy. The sealing surface may likewise be made of a high-temperature-resistant material. In order to construct the sealing configuration for achieving as great a sealing effect as possible and equilibrium between the forces (closing force, counterforce) acting on the sealing surface, the following parameters may be varied: diameter of the bellows (circularring diameter, circular-ring thickness); thickness (wall thickness) of the sealing surface and of the plates forming the bellows; clamping of the plate of the bellows, which serves for the fastening; number of plates of the bellows; diameter of the sealing surface; rigidity of the sealing surface; length and diametral position of the sealing gap; type of position; gap narrowing of the sealing elements; and fitting clearance and configuration of the transitions (connection regions) between adjacent plates.
In accordance with a concomitant feature of the invention, in addition to the sealing of a gap formed between a turbine shaft as a rotating machine component and a turbine casing part as a stationary machine component, sealing between a moving blade, in particular a complex moving-blade ring, and the turbine casing, is also made possible in one configuration of the sealing configuration. In this case, the opposing surface is preferably disposed on the moving blade and the sealing surface is preferably firmly connected to the turbine casing through the deformation region. Of course, the sealing configuration may also be disposed between a guide blade, in particular a guide-blade ring, and a turbine shaft.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a sealing configuration, in particular for a rotary machine, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.